Real-time monitoring of particles in semiconductor vacuum environment

ABSTRACT

An apparatus includes semiconductor processing equipment. A particle detecting integrated circuit is positioned in a vacuum environment, the particle detecting integrated circuit containing a device having a pair of conductive lines exposed to the vacuum environment. The pair of conductive lines is spaced at a critical pitch corresponding to diameters of particles of interest. A computer system is linked to the particle detecting integrated circuit to detect a change in an electrical property of the conductive lines when a particle becomes lodged between or on the lines.

TECHNICAL FIELD

This invention relates to real-time monitoring of particles in asemiconductor vacuum environment.

BACKGROUND

A microprocessor is an integrated circuit (IC) built on a tiny piece ofsilicon. A microprocessor contains millions of transistorsinterconnected through fine wires made of aluminum or copper.

Microprocessor fabrication is a complex process involving many steps.Microprocessors are typically built by layering materials on top of thinrounds of silicon, called wafers, through various processes usingchemicals, gases and light. In chip making, very thin layers ofmaterial, in carefully designed patterns, are put on the blank siliconwafers. The patterns are computerized designs that are miniaturized sothat up to several hundred microprocessors can be put on a single wafer.

Because the patterns are so small, it is nearly impossible to depositmaterial exactly where it needs to be on the wafer. Instead, a layer ofmaterial is deposited or grown across an entire wafer surface. Then, thematerial that is not needed is removed and only the desired patternremains.

The microprocessor fabrication process begins with “growing” aninsulting layer of silicon dioxide on top of a polished wafer in a hightemperature furnace.

Photolithography, a process in which circuit patterns are printed on thewafer surface, is next. A temporary layer of a light sensitive materialcalled a “photoresist” is applied to the wafer. Ultraviolet light shinesthrough clear spaces of a stencil called a “photomask” or “mask” toexpose selected areas of the photoresist. Masks are generated during adesign phase and are used to define a circuit pattern on each layer of achip. Exposure to light chemically changes the uncovered portions of thephotoresist. The machine used to do this is typically called a “scanner”because it scans one die or a few die at a time, then steps to the nextdie or set of die until it has exposed the entire wafer.

An active area of the mask is exposed to a vacuum environment of ascanner and is at high risk of accumulating particles. If a particlelands in a critical part of the active area then it will lead to aprinted defect on the wafer. This defect causes decreased yields, orincreased wafer cost in rework if the defect is fortuitously caughtprior to further wafer processing by wafer defect metrology.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an exemplary optical projection lithographysystem.

FIG. 2 is a block diagram of a stage.

FIG. 3 is a block diagram of an exposed semiconductor component.

FIG. 4 is a flow diagram of a real-time particle monitoring process.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The systems and techniques described here relate to real-time monitoringof particles in vacuum environments of semiconductor processingequipment. For ease of discussion, a photolithography process of asemiconductor fabrication is used as an example for describing thereal-time monitoring of particles in vacuum chambers of semiconductorprocessing equipment. However, the systems and techniques describedherein are not limited to photolithography; rather, they can be used inany semiconductor vacuum process environment in which a real-timemonitoring of particles is needed, such as while depositing a film on asemiconductor wafer or implanting a dopant on a semiconductor wafer.

A semiconductor manufacturing process hinges on a use of a photographicprocess to generate fine featured patterns of an integrated circuit(IC).Each layer of a chip is defined by a specific mask. A mask is somewhatlike a photographic negative, which is made by patterning a film ofchromium on a pure quartz glass plate. The finished plates are referredto as reticles. Peticles are manufactured by sophisticated and expensivepattern generation equipment, which is driven from a chip designdatabase. The patterns are formed on the chromium plated quartz byremoving the chromium with either laser or electron-beam driven tools.

Referring to FIG. 1, an exemplary optical projection lithography system10, such as an extreme-ultraviolet (EUV) lithography system, is shown.Optical projection lithography is the technology used to print theintricate patterns that define integrated circuits onto a semiconductorwafer 12. The system 10 includes an illuminator enclosure 14, amask-stage chamber 16, a camera chamber 18 and a wafer-stage chamber 20.

The illuminator enclosure 14 includes laser optics that, for example,generate EUV light from a plasma generated when a laser illuminates ajet of xenon gas. The light is collected and focused on a mask 22residing on a mask stage 24 in the mask-stage chamber 16 by a series ofcondenser mirrors 26 a, 26 b, 26 c, 26 d. A mask image is projected ontothe wafer 12 by a reduction camera 28 a, 28 b, 28 c, 28 d, while themask 22 and wafer 12 are simultaneously scanned. The entire operationtakes place in high-vacuum environmental chambers and is controlled by acomputer system 29.

Impurities 32, such as metallic and/or non-metallic particles, can bepresent in the mask-stage chamber 16. If one of the particles 32 landson a critical part of an active area of the mask 22 it will lead to aprinted defect on the wafer 12. This defect causes decreased yields, orincreased wafer cost in rework if the defect is detected at an earlystage. The present invention provides a real-time detection of thepresence of particles in the vicinity of the mask 22 that would warrantstoppage of the lithography system 10. In an extreme-ultraviolet (EUV)lithography environment, particle sizes that are estimated to be ofconcern are on the order of 50 nanometers (nm).

As shown in FIG. 2, the mask stage 24 includes a placement of one ormore active semiconductor components 30 near the mask 22 and embeddedwithin the mask stage 24. The active semiconductor components 30 caninclude any number of different devices that function to detectparticles that land on them.

As shown in FIG. 3, each active semiconductor component 30 includes oneor more devices 31. Each device 31 includes a pair of conductive lines34, 36 exposed to a local vacuum environment within the mask-stagechamber 16. The conductive lines 34, 36 of the device 31 are spaced at acritical pitch corresponding to the smallest particle diameter ofinterest. A voltage is applied to the conductive lines 34, 36 of thedevice 31. A metallic particle having a diameter the size of the pitchbetween the conductive lines 34, 36, or larger, generates a short in acurrent flow between the conductive lines 34, 36. A non-metallicparticle having a diameter the size of the pitch between the conductivelines 34, 36, or larger, generates a change in capacitance between theconductive lines 34, 36. The short and/or change in capacitance isdetected by the computer system 29. Detection of such particles(s)provides a warning that particles are in the vicinity of a critical partof the tool, such as near the mask 22 in this lithography example. Whendetected, corrective action can be taken, such as terminating thelithography process before the particles cause imperfections in thewafer 12. In one particular embodiment, the short and/or change incapacitance is detected by off-chip circuitry (not shown).

A number of these devices 31 can be located in the semiconductor device30 providing determination of particle density counts. Devices 31sensitive to various particle sizes, e.g., by varying the pitch of thepairs of lines, can also be incorporated into the active semiconductorcomponent 30 to monitor a range of particle sizes through a region orregions of interest.

In a particular embodiment, each active semiconductor component 30 isprotected by a remote-controlled removable cover (not shown) until thecomponent 30 is ready to be exposed to a vacuum environment. The coveris remotely triggered by the computer system 29 or other triggeringmechanism (not shown) to open when desired, exposing the device 31 tothe vacuum environment.

As shown in FIG. 4, a real-time monitoring process 100 for detectingparticles in a semiconductor vacuum environment includes exposing (102)a particle detecting integrated circuit embedded in a stage to residualgases and particles within a vacuum environment. The particle detectingintegrated circuit includes a device having a pair of conductive linesspaced at a critical pitch corresponding to diameters of particles ofinterest.

Process 100 applies (104) a voltage to the pair of conductive lines anddetects (106) a change in an electrical property of the conductive linesresulting from a particle landing on or between the pair of conductivelines. A metallic particle having a diameter the size of the pitchbetween the lines, or larger, generates a short in a current flowbetween the lines. A non-metallic particle having a diameter the size ofthe pitch between the lines, or larger, generates a change incapacitance between the lines. The short and/or change in capacitance isdetected by the computer system. Once detected, corrective action can beinitiated.

Other embodiments are within the scope of the following claims.

1-29. (canceled)
 30. An apparatus comprising: a vacuum chambercontaining a particle detecting integrated circuit, the particledetecting integrated circuit including a plurality of devices to detectparticles of different diameters, each of the plurality of devicesincluding a pair of conductive lines that are configured to define achannel to capture at least one particle having an associated one of thediameters, with the pair of conductive lines of each of the plurality ofdevices includes a uniform pitch representing a single particle sizebetween pairs of the conductive lines of the plurality of devices;wherein the pairs of the conductive lines of the plurality of devicesare further configured to enable a change in current flowing between oneof the pairs of conductive lines of the plurality of devices when ametallic particle shorts the one of the pairs of the conductive lines ofthe plurality of devices.
 31. The apparatus of claim 30 furthercomprising a computer system linked to the particle detecting integratedcircuit.
 32. The apparatus of claim 31 wherein the computer system isconfigured to detect the change in current when the metallic particleshorts the one of the pairs of conductive lines of one of the pluralityof devices.
 33. The apparatus of claim 30 wherein the particle detectingintegrated circuit includes a remote-controlled movable cover protectingthe plurality of devices.
 34. An apparatus comprising: a mask stage in avacuum chamber of semiconductor processing equipment; a particledetecting integrated circuit embedded in the mask stage, the particledetecting integrated circuit comprising a plurality of devices to detectparticles of different diameters, each of the plurality of deviceshaving a pair of conductive lines exposed to a local vacuum environment,the pair of conductive lines are configured to define a channel tocapture at least one particle having an associated one of the differentdiameters, with the pair of conductive lines of each of the plurality ofdevices having a uniform pitch representing a single particle size;wherein the pairs of conductive lines of the plurality of devices arefurther configured to enable a change in current flowing between one ofthe pairs of conductive lines of the plurality of devices when ametallic particle shorts the one of the pairs of conductive lines of theplurality of devices.
 35. The apparatus of claim 34 wherein the pair ofconductive lines of each of the plurality of devices is configured toreceive an applied voltage.
 36. The apparatus of claim 34 furthercomprising a computer system linked to the particle detecting integratedcircuit.
 37. The apparatus of claim 36 wherein the computer system isconfigured to detect the change in current when the metallic particleshorts the one of the pairs of conductive lines of the plurality ofdevices.
 38. The apparatus of claim 36 wherein the computer system issemiconductor component circuitry.
 39. The apparatus of claim 36 whereinthe computer system is off-chip circuitry.
 40. An apparatus comprising:a vacuum chamber containing a particle detecting integrated circuit, theparticle detecting integrated circuit including a plurality of devicesto detect particles of different diameters, each of the plurality ofdevices including a pair of conductive lines that are configured todefine a channel to capture at least one particle having an associatedone f the different diameters, with the pair of conductive lines of eachof the plurality of devices includes one of a plurality of pitchesrepresenting a range of particle sizes between pairs of the conductivelines of the plurality of devices; and wherein the pairs of conductivelines of the plurality of devices are further configured to enable achange in current flowing between one of the pairs of the conductivelines of the plurality of devices when a metallic particle shorts theone of the pairs of the conductive lines of the plurality of devices.41. The apparatus of claim 40 further comprising a computer systemlinked to the particle detecting integrated circuit.
 42. The apparatusof claim 41 wherein the computer system is configured to detect thechange in current when the metallic particle shorts the one of the pairsof the conductive lines of the plurality of devices.
 43. The apparatusof claim 40 wherein the particle detecting integrated circuit includes aremote-controlled movable cover protecting the plurality of devices. 44.An apparatus comprising: a mask stage in a vacuum chamber ofsemiconductor processing equipment; a particle detecting integratedcircuit embedded in the mask stage, the particle detecting integratedcircuit comprising a plurality of devices to detect particles ofdifferent diameters, each of the plurality of devices having a pair ofconductive lines exposed to a local vacuum environment, the pair ofconductive lines are configured to define a channel to capture at leastone particle having an associated one of the diameters, with the pair ofthe conductive lines of each of the plurality of devices having anon-uniform pitch representing a range of particle sizes; wherein thepairs of the conductive lines of the plurality of devices are furtherconfigured to enable a change in current flowing between one of thepairs of the conductive lines when a metallic particle shorts the one ofthe pairs of the conductive lines of the plurality of devices.
 45. Theapparatus of claim 44 wherein the pair of conductive lines of each ofthe plurality of devices is configured to receive an applied voltage.46. The apparatus of claim 44 further comprising a computer systemlinked to the particle detecting integrated circuit.
 47. The apparatusof claim 46 wherein the computer system is configured to detect thechange in current when the metallic particle shorts the one of the pairsof conductive lines of the plurality of devices.
 48. The apparatus ofclaim 46 wherein the computer system is semiconductor componentcircuitry.
 49. The apparatus of claim 46 wherein the computer system isoff-chip circuitry.